Cheap strong dye with COOH group?

Dr Engelbert Buxbaum via (by engelbert_buxbaum from
Mon Aug 8 18:56:42 EST 2011

In article <j1lokm$c74$1 from>, novalidadress from 
> At Sun, 07 Aug 2011 04:04:41 +0000, DK wrote:
> > I actually didn't know that "regular" fluorescein has carboxy group.
> > What I meant was its carboxy derivative has another COO- on the same
> > ring. Fluorescein does bleach rather easily, so this might be a turn
> > off.
> Stupid me. The carboxy group I thought of is part of the chromophore. But 
> that probably means that activating a second carboxy group for coupling 
> (by eg a carbodiimide method) might result in a mess. That might be the 
> reason, why fluorescin usually is used as isothiocyante (FITC) for 
> labelling. 
> Your suggestion with the food colorings might be worth a try. 
> Thnkns!
> Wo
> > 
> > Another thought: food coloring dyes. Of what Wikipedia lists, two
> > (erythrosine and tartrazine) are carboxylates. They should be very
> > cheap!
> > 
> > DK

FITC is used as the isothiocyanate group is very reactive towards 
primary amines, allowing protein modification under mild conditions. The 
resulting thiourea, however, has a somewhat limited stability. 

Erythrosine btw is tetraiodo-fluoresceine. 

If you plan experiments involving fluorescent labelling, your first stop 
should be the the Molecular Probes Handbook 
The-Handbook.html). For a more systematic introduction, you may also 
consider "Biophysical Chemistry of Proteins" (Springer 2011) by yours 

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